A gage of the arm type wherein an elongated member having a feeler or finger for engaging a part to be measured is commonly supported upon a column or guide rail wherein the position of the gage arm, or supporting structure, may be measured with respect to a predetermined location to produce a measurement reading. Various types of such gages are well known and the measurements produced may be visually observed and read, or may be electronically indicated, such as with digital readout apparatus. Such gaging devices utilize columns, guides and bearings which accurately support the gage arm or probe and must be maintained in a clean condition free from foreign matter if the accuracy of the measurement is to be consistent over extended durations.
It is known to use protective shields or screens with gaging apparatus employing gaging arms and probes to protect the critical portions of the gage from contamination from coolants, oil, metal chips, dirty air and the like. For instance, protective screens and shields are known which utilize a slit parallel to the gage arm path of movement through which the arm extends and resilient lips or baffles which line the slit tend to encompass the arm during its movement and prevent the entry of foreign matter through the slit. Also, it is known to use flexible screens, bellows, lapped plates, and the like which are attached to the gage arm and expand and contract, and change dimension in order to follow the gage arm movement.
While the aforementioned protective screens for gage arms, within limits, provide reasonably effective protection of the gage arm support, bearings, guideways, etc., the protective apparatus for the gage arm will impose upon the gage arm a resistance to movement which may have an adverse effect on the measurement being conducted. For instance, wherein the gage arm is supporting the weight of the protective shield, or the movement of the gage arm through a slot is impeded by the necessity to displace flexible baffles, such forces may be imposed upon the gage arm at the point of contact with the workpiece being measured preventing a consistent measurement in that the pressure of engagement between the gage and article being measured must be constant and free of external influence.
It is an object of the invention to provide gage positioning and protective apparatus wherein the protective apparatus shields gage structure from contamination by foreign matter and yet imposes no external influence on the gaging apparatus as to adversely affect the gaging procedure.
Another object of the invention is to provide gage positioning apparatus for a linear movable gage arm wherein protective apparatus is linearly positionable by power drive means and wherein the relative positions between the gage apparatus and protective structure is sensed by means controlling the power drive to automatically produce a predetermined relationship between the gage and protective structure.
An additional object of the invention is to provide a linear movable gage having protective structure wherein the protective apparatus is positioned by power drive means automatically controlled by sensing apparatus producing a predetermined relationship between the gaging and protective structure, and wherein the protective structure is interconnected by lost motion and a counterbalancing linkage.
In the practice of the invention, a gage arm or probe is mounted for linear displacement upon a column by means of a low friction bearing. Measuring apparatus is associated with the gage arm, which may be either of a mechanical, optical, or electrical construction wherein the position of the gage arm may be accurately determined for measurement purposes.
The gage arm extends through a protective shield, or surround, which includes a protective shield interposed between the gage bearing and column and the contaminating environment, and the protective apparatus is movable through a linear path corresponding to the operative path of movement of the gage arm.
The protective shield, in the disclosed embodiment, is positioned by an electrically powered drive consisting of a threaded shaft bidirectionally rotated by a reversible electric motor. Sensors mounted upon the protective shield at the location where the gage arm extends through the shield determine the relative position between the shield and gage arm and control the electric motor drive to produce a predetermined relationship between the gage arm and shield during gaging operation to insure that the shield does not impose an external influence upon the gage arm during the measuring process.
The gage arm may be moved upon its column by independent drive means, and in such instance, the protective shield apparatus will "follow" the movement of the gage arm under the control of the sensors which maintain the desired relationship between the gage arm and protective shield through operation of the shield power drive.
However, it is also possible to position the gage arm to the gaging position by the protective shield apparatus and the drive means therefor. This embodiment utilizes a lost motion and counterbalancing interconnection between the protective structure and the gage arm support which permits the protective shield drive means to function as the power positioning apparatus for both the gage arm and the protective support. In the described embodiment, the lost motion and counterbalancing connection between the protective structure and gage arm is achieved by tension springs.